Time of Emergence and Large Ensemble Intercomparison for Ocean Biogeochemical Trends

Area of Science:

• Oceanography
• Climate Science
• Biogeochemistry

Background:

• Anthropogenic changes impact ocean biogeochemistry, affecting the carbon sink and marine ecosystems.
• Detecting these changes necessitates quantifying the human-induced signal against natural climate variability (noise).

Purpose of the Study:

• To estimate the Time of Emergence (ToE) for anthropogenic signals in key ocean biogeochemical variables.
• To partition projection uncertainty, including internal variability and model differences, for these signals.

Main Methods:

• Utilized Large Ensemble (LE) experiments from four Earth system models (ESMs).
• Employed multiple emissions scenarios to analyze five upper-ocean biogeochemical variables.
• Estimated ToE and quantified uncertainty sources.

Main Results:

• Sea surface temperature and anthropogenic carbon invasion show robust ToEs (20-30 years) across models.
• Biological carbon pump, sea surface chlorophyll, and salinity have longer, less robust ToEs (50+ years), sensitive to scenarios.
• Internal variability and model differences significantly contribute to projection uncertainty.

Conclusions:

• This study provides a comprehensive characterization of biogeochemical emergence timescales and uncertainties.
• Findings highlight the need for specific spatial and temporal scales in marine observing systems to detect anthropogenic change.
• Understanding emergence times is crucial for effective ocean carbon sink management and marine habitat protection.